What's the most defensive opening?

stonewall, Anglo-slav, semi-slav, philidor, hippo, hedgehog

2 votes for stonewall... that's why I hate playing it. I'm an attacker and it's like a straightjacket trying to get your pieces swinging, but it's hard for your opponents to get to you too. Even as a 1400, it was easy to last 35 moves against fritz6, but then again, f6 loved playing pieces then retrating them. I thought crafty was way more aggressive and used that for analysis.

Probably the French Defence. In almost every line white can choose (both mainlines and sidelines) he is able to play for an attack on black's king. It's a good opening, but if you play the French you'd better be a good defender.

Also, the Stonewall is not a defensive opening. It is black who gets to attack more often than white, with a knight on e4, Queen on h5, etc. Black's main worry in the Stonewall is landing in a positionally bankrupt ending, he very rarely gets attacked.

hippo

London

Petrof. The only major attack you have know to defend is the Cochrane gambit, which is a bit hilarious. Then just know a few themes and get your pieces on the right squares and that's it. If they castle queenside then you'll have to take care but they shouldn't get a good attack that way, and as in any opening you'll be looking for a counterattack on their castled queenside.

No such thing. Every opening either loses or counter-attacks. Given enough time, your opponent will always be able to break through with perfect play, hence why space is an advantage.

Stonewall is NOT a defensive opening. Black often attacks fairly quickly with an ...a7-a5-a4 break or ...f5-f4 break. There is also a line where Black doesn't castle, and once White plays Bb2, Ba3, or e3, Black plays h5

1.d4 e6 2.c4 f5 3.g3 Nf6 4.Bg2 d5 5.Nf3 Be7 6.O-O Ne4, and after the natural 7.b3, Black plays 7...Nc6 8.Ba3 Bf6 followed by 9...h5!

For black against 1. e4, caro kann, french, and petroff come to mind. 
For black against 1. d4, the QGD, Slav, and maybe even queens indian come to mind.

Then again im 750 lol

against 1.e4 the Petrov. the Muzio line is so dry its like eating cardboard pretending to be unsalted crackers. against 1.d4 the QGA. it is a positional minefield but if navigate it right, the positions are so even that you never know who's winning.

stonewall. I like to attack and it's impossibly frustrating to get around the e6 pawn. However, this structure seems to be surprisingly resilietn for those who like it..

True, but your opponent can spice things up with the cochrane gambit.

Again, the opponent can choose sharper lines, such as the fantasy or the bayonet.

Incidentally, can someone tell me the moves of the Muzio line of the Petrov?